Presently methods involving cryogenic distillation techniques are available to purify carbon monoxide or hydrogen and carbon monoxide as separate products. These techniques are relatively energy and capital intensive. Adsorptive processes have not been successfully utilized to purify carbon monoxide or hydrogen and carbon monoxide separately because adsorbents were generally unavailable for separating carbon monoxide from hydrogen and methane containing streams. Carbon dioxide contained in such streams from which carbon monoxide is desired to be resolved also constitutes a technical difficulty for adsorptive type separations. Carbon monoxide is typically produced and recovered from synthesis gases from one of several well understood reforming methods including: steam-methane reforming, auto-thermal reforming, oxygen reforming, dry carbon dioxide reforming, partial oxidation and combinations of the above reformation reactions. Typically, the synthesis gas produced from these reformation reactions contains hydrogen, carbon monoxide, carbon dioxide, methane, water, and possibly nitrogen and argon. This synthesis gas is typically cooled in several heat exchangers to raise steam, preheat reformer feed, preheat boiler feedwater and heat makeup water. The cooled reformer synthesis gas then enters a typical carbon dioxide removal system wherein carbon dioxide is separated from the synthesis gas. The carbon dioxide removal system typically consists of chemical absorption of carbon dioxide into a liquid solvent which is regenerated in a stripping column. This system normally uses a solvent selected from the group consisting of MEA, MDEA, Benfield or other solvent systems well known in the prior art.
In the case of recovery of carbon monoxide alone, the carbon dioxide stripped synthesis gas leaving the carbon dioxide removal system would enter a drier where water and residual carbon dioxide are removed down to ppm levels. The water and carbon dioxide-free synthesis gas from the drier then enters a cryogenic distillation system where pure carbon monoxide is recovered. Also leaving the cryogenic distillation system are two or more streams containing hydrogen, carbon monoxide and/or methane.
In the case of the co-production of both hydrogen and carbon monoxide as separate product streams, the stream leaving the carbon dioxide removal system is similarly cleansed of water and carbon dioxide in a molecular sieve drier bed. Dry, carbon dioxide-free synthesis gas out of the drier is sent to a cryogenic distillation where pure carbon monoxide is recovered. Also leaving the cryogenic distillation is a carbon monoxide-methane stream that is recycled to the feed to the cryogenic distillation, as well as an impure hydrogen stream. The impure hydrogen stream typically contains low amounts (0.5% to 10%) of the carbon monoxide, and it is therefore sent to a hydrogen adsorptive system for hydrogen purification. The hydrogen adsorptive system produces a pure hydrogen stream and a low pressure carbon monoxide and hydrogen stream that is usually used as fuel.
U.S. Pat. No. 4,913,709 discloses an adsorptive process to recover high purity products, such as hydrogen and high purity carbon dioxide, as separate products from a gas mixture containing these components along with minor amounts of methane, carbon monoxide and nitrogen. Typically sodium x-zeolite is used to implement the separation.
U.S. Pat. No. 4,861,351 discloses a method for producing synthesis gas using steam-methane reforming and auto-thermal reforming wherein carbon dioxide in the resulting synthesis gas is removed with a liquid solvent of MEA (monoethanolamine) and the resulting carbon dioxide-lean synthesis gas is further resolved in a pressure swing adsorptive separation system (PSA) using typically 5A zeolite to adsorb carbon monoxide while allowing product hydrogen to pass through unadsorbed, thereby resulting in a carbon monoxide product and hydrogen product.
U.S. Pat. No. 4,171,207 discloses an adsorptive technique for recovering hydrogen unadsorbed from additional components of a gas mixture containing the hydrogen which additional components are adsorbed.
U.S. Pat. No. 4,077,779 discloses another adsorptive separation system for resolving preferably a hydrogen-containing gas mixture into a hydrogen product and a byproduct such as carbon dioxide and/or methane. Relevant adsorbents can be activated, molecular sieve carbons, silica gel, activated alumina or mixtures of these components.
U.S. Pat. No. Re. 31,014 discloses an adsorptive separation of a gas mixture to recover preferably unadsorbed hydrogen as a primary pure product as well as carbon dioxide as a separate byproduct and a waste stream containing methane, carbon monoxide and nitrogen.
U.S. Pat. No. 3,564,816 discloses an adsorptive separation process for recovering hydrogen from adsorbable components consisting of carbon monoxide, carbon dioxide, methane, light saturated or unsaturated hydrocarbons, ammonia, hydrogen sulfide, argon nitrogen and water.
U.S. Pat. No. 4,705,541 discloses an adsorptive process for processing gas mixtures, such as synthesis gas, from a steam-methane reformation reaction wherein separate high purity products of hydrogen and carbon monoxide are produced. The patent references the necessity of removing other synthesis gas components, such as carbon dioxide, before the instigation of the patented process. Typical adsorbents include A, X or Y-zeolites or mordenite with various cation exchange levels, as well as activated carbons, selective for carbon monoxide adsorption.
U.S. Pat. No. 3,150,942 discloses a method for recovering hydrogen from the reformation reaction of natural gas and steam wherein the resulting synthesis gas is subjected to water gas shift to convert carbon monoxide to hydrogen and carbon dioxide and the carbon dioxide is optionally removed by solvent extraction before the synthesis gas is subjected to pressure swing adsorptive separation of non-hydrogen components in 13X and 5A-zeolite sequentially to result in a hydrogen product and a carbon dioxide, water and carbon monoxide byproduct.
U.S. Pat. No. 4,914,218 also resolves a gas mixture to two separate products, such as resolving a combination of H.sub.2 and CO.sub.2 with other gas constituents into separate H.sub.2 and CO.sub.2 products.
U.S. Pat. No. 4,915,711 discloses a four or five step process for resolving a binary gas mixture into two separate products, such as resolving a combination of H.sub.2 and CO.sub.2 into separate H.sub.2 and CO.sub.2 products.
U.S. Pat. No. 3,699,218 discloses a process for recovery of hydrogen from a reformation product gas. Carbon dioxide is removed by methanol solvent, and carbon monoxide is removed by low temperature adsorption on sodium X zeolite. The carbon monoxide content of the reformation product gas is only up to 4.0%.
U.S. Pat. No. 4,726,816 discloses a process in which CO2, CO and H2 are all resolved in the same adsorption bed with the use of a displacement gas to fractionate the recovery of the three separate products during a single cycle of the adsorption bed.
E.P. Patent 0 317 235 discloses a process for recovering CO2, CO and H2 by the use of multiple beds of adsorbent in which CO2 must be adsorbed first. The CO product is extracted from two beds in series and then must be further refined in additional beds which upgrade the CO rich initial product to a high purity product.
E.P. Pat. 0 367 618 discloses a process in which CO2, CO and H2 are all resolved into separate products in the same adsorption bed by the use of multiple steps of desorption or depressurization.
U.S. Pat. No. 4,587,114 discloses a process for removing carbon monoxide from mixed gases using copper salts which are solvent impregnated on a carbon support.
U.S. Pat. No. 4,470,829 discloses an adsorbent for carbon monoxide comprising copper in its monovalent state supported on a carbon base wherein additionally trivalent aluminum is also included in the adsorbent.
U.S. Pat. No. 4,019,879 discloses a zeolitic molecular sieve containing monovalent copper cations which exhibit a high degree of selectivity and affinity for carbon monoxide molecules, wherein carbon monoxide may be separated from gas streams even in the presence of water vapor. Relevant gas streams may comprise carbon monoxide, water vapor, carbon dioxide or nitrogen or alternatively carbon monoxide, carbon dioxide and hydrogen.
U.S. Pat. No. 3,789,106 discloses a method for removal of low levels of carbon monoxide impurity from a gas mixture by utilizing adsorption of the carbon monoxide on mordenite charged with copper. The gas mixture may additionally contain hydrogen, nitrogen, methane, oxygen and rare gases.
U.S. Pat. No. 4,914,076 discloses a carbon monoxide selective adsorbent comprised of copper impregnated on an alumina or silica-alumina substrate. The carbon monoxide selective adsorbent may be utilized on various gas mixtures potentially containing oxygen, methane, hydrocarbons and minor components, such as hydrogen sulfide and ammonia. The recovery of carbon monoxide using the copper containing adsorbent preferably involves initial removal of sulfur compounds, ammonia, water and oxygen, but does not require the removal of carbon dioxide and nitrogen.
U.S. Pat. No. 4,713,090 discloses an adsorbent selective for carbon monoxide adsorption wherein the adsorbent comprises a composite of silica and/or alumina with a layer of activated carbon upon which a copper compound is carried. The adsorbent is useful for recovering carbon monoxide from gas mixtures containing oxygen, methane, hydrocarbons, water and small amounts of hydrogen sulfide and ammonia. Desirably the sulfur, ammonia, water and oxygen removal precede contact of the gas mixture with the copper containing adsorbents for carbon monoxide separation and recovery.
U.S. Pat. No. 4,917,711 discloses an adsorbent for selective adsorption of carbon monoxide from gas mixtures wherein the adsorbent is produced from heating of a solid mixture of a copper compound and a support having a high surface area. The adsorbent is effective for recovering carbon monoxide from a gas mixture, which may include one or more of hydrogen, nitrogen, argon, helium, methane, ethane, propane and carbon dioxide.
The prior art has identified various techniques for recovery of hydrogen individually or hydrogen and carbon dioxide from gas mixtures, as well as the recovery of carbon monoxide. However, the prior art has failed to suggest an integrated process for producing dual products of hydrogen and carbon monoxide from a gas stream containing these components, as well as carbon dioxide and methane in an energy efficient format which enhances the production of carbon monoxide. The present invention as set forth below achieves the energy efficient production of dual products using a series of related unique process integrations.